1. Field of the Invention
This invention broadly relates to an appliance used in the course of orthodontic treatment to correct a malocclusion. More particularly, the present invention relates to an orthodontic bracket having at least one tiewing for ligating an archwire to the bracket.
2. Description of the Related Art
Orthodontic treatment involves movement of a patient's teeth to improved positions. Orthodontic treatment can improve the patient's occlusion, so that the teeth function better with each other during mastication. Orthodontic treatment can also greatly enhance a patient's facial appearance, especially in instances where the teeth adjacent the front of the oral cavity are noticeably crooked.
One type of orthodontic treatment system includes a set of tiny appliances known as brackets that are fixed to the patient's anterior, cuspid and bicuspid teeth. Each of the brackets has a slot to receive a resilient wire known as an archwire. The archwire functions as a track to guide movement of the brackets and hence movement of the associated teeth to desired positions. Ends of the archwire are often received in passages of small appliances known as buccal tubes that are fixed to the patient's molar teeth.
Orthodontic brackets often have small arms or wings known as tiewings that are adjacent the archwire slot. A groove extends behind each tiewing for receiving a ligature. In use, the practitioner extends the ligature behind one or more of the tiewings and also over the archwire in order to retain the archwire in the archwire slot. If the practitioner elects to replace the archwire during the course of treatment, the ligature is removed from its position behind the tiewings in order to release the archwire from the archwire slot.
In general, two types of orthodontic ligatures are in common use. One type of ligature resembles a tiny elastomeric O-ring, and is stretched during installation to fit behind the tiewings as well as over the archwire. When the elastomeric ligature is released, it contracts to hold the archwire in place. Another type of orthodontic ligature in common use is made of a segment of small-diameter metallic wire, and ends of the wire are twisted together to form a snug-fitting loop after the wire has been extended behind the selected tiewings and over the archwire.
Over the years, there has been increased interest in improving the aesthetics of orthodontic appliances so that the appliances are less noticeable during the course of treatment. Many attempts have been made to reduce the size of orthodontic appliances, and some ceramic appliances are as small as, for example, 3.5 mm in height and 3.0 mm in width. However, attempts to reduce the overall size of the bracket are often hampered at least in part by the tiewings, since the tiewings should extend outwardly a distance sufficient to reliably retain the ligature in place. If the ligature is accidentally dislodged from its position behind the tiewings, the archwire may release from the bracket with the result that the progress of treatment is interrupted.
In addition to reducing the overall size of orthodontic appliances, many manufacturers have introduced appliances made of a transparent or translucent material in order to render the appliance less noticeable and consequently more aesthetic in the oral cavity. Examples of suitable transparent and translucent materials include ceramic materials, such as monocrystalline and polycrystalline alumina. Appliances made of a plastic material such as polycarbonate are also available. Preferably, the transparent or translucent materials are colorless and transmit sufficient light to take on the color of the underlying tooth.
Appliances made of translucent and transparent ceramic materials are preferred by many practitioners. However, ceramic materials are relatively brittle and lack strength in tension. If the tiewings of ceramic brackets are too small, they may fracture when exposed to unexpectedly large forces during the course of treatment.
As can be appreciated, there is a continuing need in the art for an orthodontic bracket that is considered aesthetic by both the practitioner and the patient, and yet is constructed such that the probability of tiewing fracture is reduced.